mos

Small x86 hobby OS experiment built from a Multiboot entry stub, a 64-bit bootstrap path, and a Mojo kernel.

What is here

• boot.s: Multiboot header and early bootstrap that enables paging and jumps into long mode.
• stubs.s: Runtime shims expected by the Mojo toolchain plus the inb wrapper used for keyboard input.
• kernel.mojo: VGA plus serial-console kernel prototype with a tiny Linux-shaped process model.
• linker.ld: Kernel linker script placing the image at 1 MiB.
• Makefile: Rebuilds the kernel with the checked-in Mojo SDK and system assembler/linker.
• build.sh: Shell build path using the exact commands verified in this repo.

Current behavior

The kernel:

• enters 64-bit mode from the Multiboot loader
• writes directly to VGA text memory at 0xb8000
• initializes COM1 and mirrors console output to serial
• exposes four process slots with PID, PPID, state, and tick counters
• boots with pid 1 = init and pid 2 = kthreadd
• models runnable, sleeping, stopped, and zombie task states
• lets init reap zombies and reparent tasks when their parent exits

Current serial controls:

• h: help
• s: spawn a worker under init
• n: select the next non-empty slot
• t: run one scheduler tick on the selected task
• p: toggle stop/run for the selected task
• z: toggle sleep/wake for the selected task
• k: terminate the selected task into zombie state
• r: let init reap one zombie
• 1 2 3 4: directly select a slot

This is still a prototype. It is not close to Linux feature parity: there is no memory management subsystem, userspace ABI, ELF loader, syscall layer, VFS, driver model, interrupts, or real init process execution. What exists now is a small step toward that shape, not a 1:1 Linux clone.

Existing build artifacts

This repository currently contains generated outputs from local builds:

• boot.o
• stubs.o
• kernel.o
• kernel64.bin
• myos.bin
• kgen.trace.json.time-events.txt
• kgen.trace.json.time-trace

kernel64.bin is the reproducible linked ELF64 kernel image produced by the current Makefile.

myos.bin is a legacy checked-in artifact from an older flow and is not currently regenerated by the new build target.

Build

Run:

./build.sh

Or, if make is installed on the machine:

make

Both routes rebuild:

• boot.o from boot.s
• stubs.o from stubs.s
• kernel.s from kernel.mojo using the checked-in Mojo SDK
• kernel.o from kernel.s
• kernel64.bin from the linker script plus all objects

make clean removes the generated build outputs when make is available.

Run

Best-effort QEMU launcher:

./run-qemu.sh

Notes:

• this environment has qemu-system-x86_64
• this environment does not have grub-mkrescue or ISO tooling
• the direct QEMU ELF loader path is the only local option wired here
• the kernel build is verified; the headless QEMU boot path is still experimental and may need a proper Multiboot/GRUB handoff to be fully reliable

Next useful work

• add a real boot path with GRUB or a 32-bit Multiboot wrapper image
• replace the fixed process slots with kernel task structs and queues
• add interrupts, timers, and a real scheduler tick
• introduce a syscall boundary and a genuine init userspace program